The present invention relates to optical disk pickup device used for reading and/or recording data in optical disk systems.
FIG. 1 shows a conventional optical disk pickup device, which comprises a semiconductor laser 1 used as a light source, a grating 2 for generating sub beams to detect tracking error, a beam splitter 3 for reflecting the laser beam emitted through the grating 2 to the optical disk D an object lens 4 for focusing the laser beam reflected from the beamsplitter 3 on to the optical disk D, a cylindrical lens 5 for giving an astigmatism to generate focus error signals and for guiding the reflected laser beam from the surface of the optical disk D to photodetectors 6, and a photodetector 7 for converting guided laser beam into electric signal.
In this optical disk pickup device, the laser beam emitted from the semiconductor laser 1 is diffracted through the grating 2 to generate a main beam (0th diffraction) and two sub beams (1st and -1st) reflected by the beam splitter 3, and then focused on the surface of the optical disk D by the object lens 4.
The laser beam reflected and diffracted by the optical disk D returns to beam splitter 3, and further a part of said beam is focused on photodetector 6 by the cylindrical lens 5.
The main beam is used for detecting information signals stored in the optical disk and focus error signals, and two subbeams are used for detecting tracking error signals.
However, above mentioned conventional optical disk pickup device has the following problems.
Firstly, The size of the optical system itself is large. The number of its components is also large.
Secondly, the arrangement of the components occupies large space so that the total volume of the system becomes bigger. As a result of that, access time of the system is getting slower.